The present invention relates to an electric power steering drive control apparatus that gives an assist force to a vehicle steering gear, for example, by a rotational force of an electric motor, and more particularly, to a power module conducible to enhance heat-releasing efficiency and achieve a size reduction and a cost reduction of a control device controlling driving of an electric motor and to an electric power steering drive control apparatus integrally incorporating the power module.
Conventionally, there is provided a drive apparatus for electric power steering gear including an electric motor that outputs an assist torque to a steering wheel of a vehicle and a control device that controls the driving of the electric motor and configured in such a manner that the control device is attached to the electric motor. Also, a plurality of semiconductor switching elements forming the control device are provided integrally in modules on aboard (see, for example, Patent Document 1 and Patent Document 2).
Patent Document 1 proposes a motor drive apparatus configured in such a manner that various motors, for example, both of a brushed motor and a three-phase brushless motor, can share a plurality of switching elements by providing the switching elements in the form of integrated power modules.
Also, an electric power steering gear of Patent Document 2 reduces a radiation noise and a power loss and achieves a size reduction by fitting a power board on which are mounted heat generating components, such as a plurality of switching elements that control power of an electric motor, to a control board on which are mounted low-current components, such as a micro-computer, in lamination via a circuit case and by firmly attaching the power board to a heat sink also serving as a bracket on a side opposite to an output of a three-phase brushless motor.
In Patent Document 1, however, no consideration is given to a heat-releasing structure for heat generated from the power portion and heat generation in the power module becomes inhomogeneous.
Also, the device of Patent Document 2 improves a heat-radiation performance by laminating the control device on the back surface of the motor. However, the laminated structure causes an increase in size and cost. Also, Patent Document 2 remains silent about a layout and a configuration of power elements to improve thermal efficiency.
Further, with a type having a motor relay switching element that is provided between a plurality of power switching elements forming a bridge circuit and a motor and switches a power supply to the motor ON and OFF, a current about twice as high as that flowing through each power switching element flows through the motor relay switching element. Consequently, a temperature rise of the motor relay switching element becomes correspondingly greater than that of the other switching elements. Hence, heat generation in the power module correspondingly becomes inhomogeneous.